Abstract:
We have studied the levels of 14C in firn and ice from two regions accumulating ice in Antarctica, Dome C, and Newall Glacier. The observed concentrations indicate variable amounts of in-situ 14C from cosmic-ray spallation of oxygen. 14C appears to be produced as both CO and CO2 in variable amounts, but our results suggest rapid conversion of 14CO to 14CO2. Much of the in-situ 14C is retained ... which results in a significant modification of the 14C/12C in ice derived from trapping of air at and below the firn-ice transition zone. This means that direct dating of accumulating ice cannot be used without correction for the in-situ 14C. In Newall ice, we see some evidence for an enhancement in in-situ 14C at or near the time of the Maunder Minimum. Results for Dome C firn and ice indicate higher levels of in-situ 14C in older ice. This is due either to a reduced accumulation rate in the past, or possible variations in cosmogenic 14C production. The levels of in-situ 14C in firn and ice, and its impact on 14C dates on trapped CO2 in ice are discussed.